Field of the Invention
The invention relates to a sensing circuit, and more particularly, a sensing circuit, capable of simplifying a configuration of a data driver by reducing a size of a sensing circuit provided at each data driver, and to an organic light emitting diode (OLED) display device having the same.
Discussion of the Related Art
An organic light emitting diode (OLED) display device has advantages of fast response speed, high luminous efficiency, high brightness and a great viewing angle by virtue of using self-illuminating diodes which emit light by themselves. The OLED display device is configured in such a manner that pixels each including an OLED as such a self-illuminating diode are arranged on a display panel, and the brightness of a pixel selected by a gate signal is controlled according to a gray scale level of a data signal so as to display an image.
FIG. 1 is an equivalent circuit view of one pixel of an OLED display device according to the related art.
As illustrated in FIG. 1, each pixel P of an OLED display device includes an OLED, a gate line GL, a sensing line SL and a data line DL intersecting with one another, a first switching thin film transistor (TFT) ST1, a second switching TFT ST2, a driving TFT DT and a storage capacitor Cst.
The first switching TFT ST1 is turned on in response to a gate signal input from the gate line GL, and allows for a flow of an electric current (conducts a current) between a source electrode and a drain electrode. The first switching TFT ST1 applies a data signal input through the data line DL to the driving TFT DT and the storage capacitor Cst during its turn-on period. The second switching TFT ST2 is turned on in response to a sensing signal input from the sensing line SL, and applies a reference voltage Vref supplied through a reference line RL to an anode electrode of the OLED. The driving TFT DT controls a current which flows from a power source voltage EVDD to the OLED during its turn-on period. The storage capacitor Cst uniformly maintains a gate potential of the driving TFT DT for one frame. The OLED is connected between the driving TFT DT and a ground voltage EVSS.
The aforementioned pixel P of the OLED display device displays an image in a manner that the OLED continuously emits light for a frame section and thus the driving TFT DT is kept maintained in the turn-on state. This causes deterioration of the driving TFT DT. To solve this problem, in the related art OLED display device, a method of sensing a change of a threshold voltage Vth and a change of a characteristic of the OLED and compensating for the changes has been proposed.
FIG. 2 is a view illustrating a part of the related art OLED display device.
As illustrated in FIG. 2, the related art OLED display device includes a display panel 10 and a sensing unit.
On the display panel 10, the pixels P described in FIG. 1 are arranged in a matrix configuration.
The sensing unit includes a sampling and holding portion 20, a scaling portion 30, an amplifier 40, and an analog-digital converter 50.
The sampling and holding portion 20 is connected to a plurality of reference lines RL, namely, the second switching TFT ST2 of each pixel P. The sampling and holding portion 20 temporarily stores sensing voltages supplied through the plurality of reference lines RL, through which the reference voltage Vref is supplied, and senses a characteristic change, such as a change of a threshold voltage of the display panel 10. One sampling and holding portion 20 is connected to a preset number of reference lines RL to temporarily store the sensing voltages. A plurality of first switches SW1 are disposed between the sampling and holding portion 20 and the reference lines RL to control a supply of the sensing voltages applied from the reference lines RL to the sampling and holding portion 20. The sampling and holding portion 20 includes a second switch SW2, a third switch SW3 and a first capacitor C1, and stores a voltage in the first capacitor C1 according to switching operations of the second switch SW2 and the third switch SW3.
The scaling portion 30 is arranged to correspond to the sampling and holding portion 20 in an one-to-one manner. The scaling portion 30 adjusts the level of the sensing voltages supplied from the sampling and holding portion 20 in a manner of scaling the sensing voltages. The scaling portion 30 includes a fourth switch SW4, a fifth switch SW5 and a second capacitor C2.
The level-adjusted (or scaled) sensing voltages by the scaling portion 30 are applied to an ADC 50 via the amplifier 40. The ADC 50 outputs sensing data SD through an analog-digital conversion of the level-adjusted sensing voltages.
The sensing unit is provided at each of a plurality of data drivers each having a form of a driving integrated circuit (DIC) connected to the display panel 10.
Accordingly, one data driver of the related art OLED display device includes the sensing unit provided with the plurality of sampling and holding portions 20 and the plurality of scaling portions 30, which causes an increase in the size of the data driver.
In addition, in the related art OLED display device, a plurality of sixth switches SW6 are provided between the plurality of scaling portions 30 and the amplifier 40. The plurality of sixth switches SW6 sequentially perform a switching operation such that the scaled voltages are transferred to the ADC 50. In this instance, parasitic capacitance is generated, in response to the switching operation of the plurality of sixth switches SW6, and thereby causes errors in the scaling voltages. More errors are generated when the number of the scaling portion 30 increases, namely, the number of the sixth switch SW6 increases. This results in lowering operation reliability of the sensing unit.